Different artificial two-stage ageing behaviors and their effect on stress corrosion cracking （SCC） susceptibility of AI-Zn-Mg alloy have been investigated. The experimental results show that two hardness peaks pres...Different artificial two-stage ageing behaviors and their effect on stress corrosion cracking （SCC） susceptibility of AI-Zn-Mg alloy have been investigated. The experimental results show that two hardness peaks present on the second-stage ageing-hardening curve when the first-stage ageing is dealt with comparatively lower temperature than the conventional one. The first peak is caused by dispersive and evenly distributed G.P. zones, while η ′phases and coarsened G.P. zones contribute to the second peak. Tensile strength of experimental alloy raises 9.6% （33.2 MPa） and SCC susceptibility decreases 38.9% by applying the second peak ageing regime instead of conventional T73. AI-Zn-Mg alloy obtains high strength and SCC resistance due to its finely dispersive matrix precipitates （MPts）, coarsened and discontinuous grain boundary precipitates （GBPs）, as well as the narrow precipitate free zone （PFZ） in the second peak ageing condition. 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer)...NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer), to promote mechanical properties of the Ni Ti/SS joints. The joints with different interlayers are all fractured in the weld zone near the Ni Ti side, which is attributed to the enrichment of intermetallic compounds including Fe2 Ti and Ni3 Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding Fe Ni interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2 Ti, Ni3 Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3 Ti and Fe2 Ti will be formed when the Fe Ni alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.展开更多
The effect of compressive stress on the stability of reversed austenite in gNi steel was investigated by uni- axial and hydrostatic compression. It was found that the uniaxial compressive pressure promoted the Υ-α t...The effect of compressive stress on the stability of reversed austenite in gNi steel was investigated by uni- axial and hydrostatic compression. It was found that the uniaxial compressive pressure promoted the Υ-α transformation, while the hydrostatic pressure suppressed the -Υ-α transformation. The pressure dependent transformation behavior can be explained according to thermodynamic analysis.展开更多
Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries,while high stress corrosion cracking(SCC)suscept...Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries,while high stress corrosion cracking(SCC)susceptibility of Al-Zn-Mg alloys(especially the alloy with high recrystallization fraction)with high strength makes it difficult.In this study,the influence of tensile stress-aging coupled with natural aging pre-treatment on the mechanical properties and SCC resistance of Al-Zn-Mg alloy with high recrystallization fraction has been investigated.The results show that tensile stress-aging at 160℃can inhibit the dissolution of clusters/Guinier-Preston(GP)zones formed during long-term natural aging pre-treatment,which increases the number density of matrix precipitates(MPts),narrow the width of precipitate free zone(PFZ),and dramatically improve the mechanical properties of the experimental Al-Zn-Mg alloy.Meanwhile,the precipitation of the high density of MPts within the matrix will assume a large number of solute atoms during artificial aging,which will reduce the supplement of solute atoms to grain boundaries.As a result,the volume of anodic active grain boundary precipitates(GBPs)and the content of free solute atoms at grain boundaries are reduced,which reduces the possibility of initial nucleation and propagation of SCC crack.The coupled treatment method proposed in this study proves efficient in resolving the contradiction between the strength and SCC resistance in Al-Zn-Mg alloy.展开更多
基金financial supports by National Key R&D Program of China (No. 2016YFB1200600 and No. 2016YFB1200504)Strategic Priority Program of the Chinese Academy of Sciences (No. XDB22000000)
文摘Different artificial two-stage ageing behaviors and their effect on stress corrosion cracking （SCC） susceptibility of AI-Zn-Mg alloy have been investigated. The experimental results show that two hardness peaks present on the second-stage ageing-hardening curve when the first-stage ageing is dealt with comparatively lower temperature than the conventional one. The first peak is caused by dispersive and evenly distributed G.P. zones, while η ′phases and coarsened G.P. zones contribute to the second peak. Tensile strength of experimental alloy raises 9.6% （33.2 MPa） and SCC susceptibility decreases 38.9% by applying the second peak ageing regime instead of conventional T73. AI-Zn-Mg alloy obtains high strength and SCC resistance due to its finely dispersive matrix precipitates （MPts）, coarsened and discontinuous grain boundary precipitates （GBPs）, as well as the narrow precipitate free zone （PFZ） in the second peak ageing condition. 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
文摘NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer), to promote mechanical properties of the Ni Ti/SS joints. The joints with different interlayers are all fractured in the weld zone near the Ni Ti side, which is attributed to the enrichment of intermetallic compounds including Fe2 Ti and Ni3 Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding Fe Ni interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2 Ti, Ni3 Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3 Ti and Fe2 Ti will be formed when the Fe Ni alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.
基金supported by the National Natural Science Foundation of China under Grant No.50871110
文摘The effect of compressive stress on the stability of reversed austenite in gNi steel was investigated by uni- axial and hydrostatic compression. It was found that the uniaxial compressive pressure promoted the Υ-α transformation, while the hydrostatic pressure suppressed the -Υ-α transformation. The pressure dependent transformation behavior can be explained according to thermodynamic analysis.
基金the National Key R&D Program of China(No.2016YFB1200602)the Strategic Priority Program of the Chinese Academy of Sciences(No.XDB22020200)the Shenyang Key R&D and Technology Transfer program(No.Z19–1–004)。
文摘Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries,while high stress corrosion cracking(SCC)susceptibility of Al-Zn-Mg alloys(especially the alloy with high recrystallization fraction)with high strength makes it difficult.In this study,the influence of tensile stress-aging coupled with natural aging pre-treatment on the mechanical properties and SCC resistance of Al-Zn-Mg alloy with high recrystallization fraction has been investigated.The results show that tensile stress-aging at 160℃can inhibit the dissolution of clusters/Guinier-Preston(GP)zones formed during long-term natural aging pre-treatment,which increases the number density of matrix precipitates(MPts),narrow the width of precipitate free zone(PFZ),and dramatically improve the mechanical properties of the experimental Al-Zn-Mg alloy.Meanwhile,the precipitation of the high density of MPts within the matrix will assume a large number of solute atoms during artificial aging,which will reduce the supplement of solute atoms to grain boundaries.As a result,the volume of anodic active grain boundary precipitates(GBPs)and the content of free solute atoms at grain boundaries are reduced,which reduces the possibility of initial nucleation and propagation of SCC crack.The coupled treatment method proposed in this study proves efficient in resolving the contradiction between the strength and SCC resistance in Al-Zn-Mg alloy.
